Chemical Reactivity and Alteration of Pyrite Mineral in the Kubi Gold Concession in Ghana

Abstract

Pyrite is the most common among the group of sulfide minerals on Earth and abundant in most geological settings. This gangue mineral, in association with garnet, hematite, magnetite, and other sulfide minerals, acts as an indicator mineral in the Kubi concession of the Asante Gold corporation in Ghana. X-ray difraction (XRD), air annealing in a furnace, energy-dispersive x-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) were applied to investigate the crystal structure, identify individual elements, permanence, transformation, and chemical/electronic properties of such pyrite. The study aims to identify individual elements and gain an understanding of the surface reaction mechanisms, as well as the properties of precipitated pyrite particles observed during the hydrothermal formation of the ore deposit. XRD shows that pristine and annealed samples contain some hematite and quartz, besides pyrite. Results from air annealing indicate that the relationship between pyrite and hematite-magnetite is controlled by temperature. EDX reveals that the sample has O and C as contaminants, while XPS in addition reveals Ba, Au, P, Al, and N. These elements are attributed to pyrite, that bonds metallically or covalently to neighboring ligands/impurity minerals such as oxides and chalcogenide sulfides, as well as the gangue alteration minerals of magnetite and hematite in the pyrite sample. These findings suggest that during the hydrothermal fow regime, pyrite, pathfinder elements, and impurity minerals and metals were in contact with quartz minerals before undergoing hematite transformation, which thus becomes an indicator mineral in the Kubi gold concession.